Implantable biomedical chip with modulator for a wireless neural stimulation system

ABSTRACT

The invention relates to an implantable biomedical chip with modulator for a wireless neural stimulating system. The implantable biomedical chip comprises a power regulator, a demodulator, a baseband circuit, a D/A converter, an instrumentation amplifier, an A/D converter and a modulator. According to the invention, the modulator is mounted on the implantable biomedical chip, and can achieve full-duplex communication to improve the controllability and observability. Besides, the power consumption and area occupation is reduced as compared with using discrete components. Therefore, the integration of the implantable biomedical chip can be easily accomplished.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an implantable biomedical chip forwireless neural stimulation system, more particularly, an implantablebiomedical chip with modulator for a wireless neural stimulating system.

2. Description of the Related Art

Referring to FIG. 1, it shows a conventional wireless neural stimulatingsystem. The conventional wireless neural stimulating system 10comprises: an internal module 11 and an external module 13. The internalmodule 11 is implemented in the body. The internal module 11 comprises areceiver coil 111, a voltage rectifier and steps-down circuit 112, avoltage divider 113, a load-shift keying (LSK) modulator 114, atransmitter coil 115 and an implantable biomedical chip 12.

The implantable biomedical chip 12 comprises a power regulator 121, ademodulator 122, a decoder circuit 123, a D/A converter 124, aninstrumentation amplifier 125 and an A/D converter 126. The powerregulator 121 is used for receiving power from the receiver coil 111 andproviding power. The demodulator 122 is used for demodulating an inputsignal from the receiver coil 111 to a demodulated signal. The decodercircuit 123 is used for decoding the demodulated signal to at least onecontrol signal. The D/A converter 124 is used for converting the controlsignal to a stimulating current to the nerve. The instrumentationamplifier 125 is used for amplifying and filtering a neural signal fromthe nerve. The A/D converter 126 is used for converting the neuralsignal from the instrumentation amplifier to a digital neural signal.The digital neural signal is transmitted to the LSK modulator 114 and ismodulated to an output signal. The output signal is transmitted to theexternal module 13 by the transmitter coil 115.

In the conventional wireless neural stimulating system 10, the LSKmodulator 114 is mounted outside the implantable biomedical chip 12. TheLSK modulator 114 using discrete components is difficult to beco-simulated with the complete integrated system, and the discretecomponents occupy larger area on a PCB (printed-circuit board) and havelarger power consumption.

Therefore, it is necessary to provide an implantable biomedical chipwith modulator for a wireless neural stimulating system to resolve theabove problems.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide an implantablebiomedical chip with modulator for a wireless neural stimulating system.The implantable biomedical chip comprises a power regulator, ademodulator, a baseband circuit, a D/A converter, an instrumentationamplifier, an A/D converter and a modulator. The power regulator is usedfor receiving power from a receiver coil and providing power. Thedemodulator is used for demodulating an input signal from the receivercoil to a demodulated signal. The baseband circuit is used for decodingthe demodulated signal to at least one control signal. The D/A converteris used for converting the control signal to a stimulating current. Theinstrumentation amplifier is used for amplifying and filtering a neuralsignal. The A/D converter is used for converting the neural signal fromthe instrumentation amplifier to a digital neural signal. The modulatoris used for modulating the digital neural signal to an output signal.

According to the invention, the modulator is mounted on the implantablebiomedical chip, and can achieve full-duplex communication to improvethe controllability and observability. Besides, the power consumptionand area occupation is reduced as compared with using discretecomponents. Therefore, the integration of the implantable biomedicalchip can be easily accomplished.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional wireless neural stimulating system.

FIG. 2 shows a wireless neural stimulating system with an implantablebiomedical chip having load-shift keying (LSK) modulator according tothe invention.

FIG. 3 shows the simplified simulation model of the bi-directionaltelemetry.

FIG. 4 shows a LSK modulation, according to the invention.

FIG. 5 shows a baseband circuit of the implantable biomedical chip,according to the invention.

FIG. 6 shows a state transition method for the implantable biomedicalchip according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, it shows a wireless neural stimulating system withan implantable biomedical chip having load-shift keying modulator,according to the invention. The wireless neural stimulating system 20comprises: an internal module 21 and an external module 23. The internalmodule 21 is implemented in the body. The internal module 21 comprises areceiver coil 211, a voltage rectifier and steps-down circuit 212, avoltage divider 213, a transmitter coil 215 and an implantablebiomedical chip 22.

The implantable biomedical chip 22 comprises a power regulator 221, ademodulator 222, a baseband circuit 223, a D/A converter 224, aninstrumentation amplifier 225, an A/D converter 226 and a modulator 227.The power regulator 221 is used for receiving power from the receivercoil 211 and providing power. The demodulator 222 is used fordemodulating an input signal from the receiver coil 211 to a demodulatedsignal. The demodulator 222 may be an Amplitude Shift Keying (ASK)demodulator. The baseband circuit 223 is used for decoding thedemodulated signal to at least one control signal. The D/A converter 224is used for converting the control signal to a stimulating current tothe nerve. The instrumentation amplifier 225 is used for amplifying andfiltering a neural signal from the nerve. The A/D converter 226 is usedfor converting the neural signal from the instrumentation amplifier to adigital neural signal. The modulator 227 is used for modulating thedigital neural signal to an output signal. The demodulator 227 may be aLoad-Shift Keying (LSK) modulator. The output signal is transmitted tothe external module 23 by the transmitter coil 215.

The implantable biomedical chip 22 further comprises a clock generatorand power-on reset circuit 228, the clock generator used for generatinga clock signal to the baseband circuit 223, the power-on reset circuitused for generating a power-on reset signal to the baseband circuit 223.

Referring to FIG. 3, it shows the simplified simulation model of thebi-directional telemetry. The first resistor R₁ includes the outputresistor of the downlink modulator and the parasitic resistor. The firstcapacitor C₁ and the first inductance coil L₁ are the external resonantcircuits, while the second capacitor C₂ and the second inductance coilL₂ are the internal resonant circuits. The second resistor R₂ is theparasitic resistor. The load resistor R_(L) is the equivalent loadresistor which represents how much power is consumed by the implantablebiomedical chip 22.

According to the induction fundamental, the first voltage (u₁) in theexternal coil can be found by the multiplication of the current throughthe external coil and the induced impedance (Z_(T)), wherein Z_(T)represents the feedback from the loading of the internal coil andappears as the impedance of the external coil. Thus, the first voltageu₁ is expressed by the following equation. $\begin{matrix}{u_{1} = {{i_{1} \times Z_{T}} = {i_{1} \cdot \frac{w^{2}{k^{2} \cdot L_{1} \cdot L_{2}}}{R_{2} + {j\quad\omega\quad L_{2}} + Z_{2}}}}} & (1)\end{matrix}$

where ${Z_{2} = \frac{R_{L}}{1 + {j\quad\omega\quad R_{L}C_{2}}}},$and k is the coupling coefficient.

Because we don't care the phase response, the magnitude of the inducedimpedance is taken into consideration. $\begin{matrix}{{Z_{T}} = {\frac{w^{2}{k^{2} \cdot L_{1} \cdot L_{2}}}{f_{1}^{2} + f_{2}^{2}} \cdot \sqrt{\left( {f_{1} + {f_{2}\omega\quad R_{L}C_{2}}} \right)^{2} + \left( {{f_{1}\omega\quad R_{L}C_{2}} - f_{2}} \right)^{2}}}} & (2)\end{matrix}$

where f₁=R₂+R_(L)−w²R_(L)L₂C₂, and f₂=wL₂+wR₂R_(L)C₂.

According to Eqn. (1) and Eqn. (2), it is derived that the amplitude ofthe first voltage u₁ can be determined by the load resistor R_(L).However, changing the loading resistor R_(L) would make change in powerthat is supplied for the implantable biomedical chip. Moreover, in orderto make the voltage difference in the first voltage u₁ more obvious suchthat it can be detected more easily, a severe variation in R_(L) isrequired. It may reduce the power supplied for the implantablebiomedical chip. Thus, an on-chip switched-capacitor circuit is used asthe LSK modulator 227 to vary the induced impedance Z_(T), as shown inFIG. 4. The load-shift keying modulator 227 comprises: a transistor 41and a capacitance 42.

Implementation and simulation of the invention include the mathematicmodel and the schematic circuit. Thus, we use Verilog-AMS, which is theextension of two languages, Verilog-HDL and Verilog-A, to model theinduction formula described in the above and the operation of theexternal modulator. This work is simulated by using Spectre simulator.In the simulation, ASK modulation is used for downlink. The firstvoltage u₁ reflects the switch of the 2 pF capacitor in its amplitude.The amplitude variation of the first voltage u₁ is 24% and 2% when thevoltage in the external coil is 460 Vp-p and 250 Vp-p, respectively. Theparameters of the components in FIG. 2 and 3 are shown in TABLE I. Thepower consumption of the LSK modulator is 0.95 mW at 10 Kbps data rateand the area is 50×90 μm². TABLE I COMPONENT PARAMETERS OF STIMULATIONComponents Value L₁ 28 μH L₂ 13.55 μH C₁ 226 pF C₂ 467 pF C_(lsk) 2 pFR₁ 10μ Ω R₂ 10μ Ω R_(L) 1 MΩ K 0.4 ω 12.56M rad/s

According to the invention, the LSK modulator 227 can be included on theimplantable biomedical chip 22, and can achieve full-duplexcommunication to improve the controllability and observability. Besides,the power consumption and area occupation is reduced as compared withthe prior art using discrete components. Therefore, the integration ofthe implantable biomedical chip can be easily accomplished.

Referring to FIG. 5, the baseband circuit 223 comprises: a mixed-signalmodule 51, a data and clock recovery circuit 52, a serial to parallelconverter 53 and a decoder 54. The mixed-signal module 51 is used forgenerating a built-in clock signal and a built-in reset signal. Themixed-signal module 51 comprises: an oscillator (OSC) 511 and a built-inreset circuit 512. The oscillator 511 is used for generating thebuilt-in clock signal (5 MHz), the built-in reset circuit 512 is usedfor generating the built-in reset signal.

The data and clock recovery circuit 52 is used for generating arecovered clock signal and recovering the demodulated signal from theASK demodulator 222 to a recovered packet according to the built-inclock signal and the built-in reset signal. The serial to parallelconverter 53 for converting the recovered packet into a parallelrecovered packet. The decoder 54 is used for decoding the recoveredclock signal and the parallel recovered packet and generating an addresscontrol signal (AD), a magnitude control signal (MAG) and a polaritycontrol signal (P) to the corresponding D/A converter channels 61 or 62of the D/A converter 224.

The D/A converter channels 61 or 62 of the D/A converter 224 directlysupply stimulating currents to their associative nerves to serve as astimulus. The magnitude of the stimulating current is determined by themagnitude control signal (MAG). The polarity control signal (P) is usedto control the stimulating current direction. When AD=0, the stimulusfor nerve #0 is activated.

Referring to FIG. 6, it shows a state transition method for theimplantable biomedical chip according to the invention. There are fourstates: a zero state S0, a first state S1, a second state S2 and a thirdstate S3. Referring to FIG. 5 and FIG. 6, the built-in reset signalcircuit 512 generates the built-in reset signal. The demodulated signalfrom the ASK demodulator comprises: a synchronization packet, a startpacket, data packet and an end packet. When the built-in reset signal isat low level (0), the state does not transit and remain in the zerostate S0. When the built-in reset signal is at high level (1), the zerostate S0 is transited to the first state S1.

When the synchronization packet is received, the first state S1 istransited to the second state S2. When the built-in reset signal is atlow level (0), the first state is transited to the zero state. If thereis no data (data_in=0), the state does not transit and remain in thefirst state S1. When the synchronization packet is received, the dataand clock recovery circuit 52 counts how many cycles of the 5 MHzbuilt-in clock during each positive edge and negative edge of thesynchronization packet. The cycle numbers are recorded and then used togenerate the system clock.

When the start packet is received, the second state S2 is transited tothe third state S3. When the built-in reset signal is at low level (0),the second state S2 is transited to the zero state S0. If the startpacket is not received, the state does not transit and remain in thesecond state S2.

When an end packet is received, the third state S3 is transited to thefirst state S1. When the built-in reset signal is at low level (0), thethird state S3 is transited to the zero state S0. If the end packet isnot received, the state does not transit and remain in the third stateS3 for receiving data packets.

While an embodiment of the present invention has been illustrated anddescribed, various modifications and improvements can be made by thoseskilled in the art. The embodiment of the present invention is thereforedescribed in an illustrative, but not restrictive, sense. It is intendedthat the present invention may not be limited to the particular forms asillustrated, and that all modifications which maintain the spirit andscope of the present invention are within the scope as defined in theappended claims.

1. An implantable biomedical chip with modulator for a wireless neuralstimulating system, comprising: a power regulator, for receiving powerfrom a receiver coil and providing power; a demodulator, fordemodulating an input signal from the receiver coil to a demodulatedsignal; a baseband circuit, for decoding the demodulated signal to atleast one control signal; a D/A converter, for converting the controlsignal to a stimulating current; an instrumentation amplifier, foramplifying and filtering a neural signal; an A/D converter, forconverting the neural signal from the instrumentation amplifier to adigital neural signal; and a modulator, the for modulating the digitalneural signal to an output signal.
 2. The implantable biomedical chipaccording to claim 1, further comprising a clock generator and power-onreset circuit, the clock generator used for generating a clock signal tothe baseband circuit, the power-on reset circuit used for generating apower-on reset signal to the baseband circuit.
 3. The implantablebiomedical chip according to claim 1, wherein the baseband circuitcomprises: a mixed-signal module, for generating a built-in clock signaland a built-in reset signal; a data and clock recovery circuit, forgenerating a recovered clock signal and recovering the demodulatedsignal to a recovered packet according to the built-in clock signal andthe built-in reset signal; a serial to parallel converter, forconverting the recovered packet into a parallel recovered packet; adecoder, for decoding the recovered clock and the parallel recoveredpacket and generating an address control signal, a magnitude controlsignal and a polarity control signal.
 4. The implantable biomedical chipaccording to claim 3, wherein the mixed-signal module comprises: anoscillator and a built-in reset circuit, the oscillator is used forgenerating the built-in clock signal, the built-in reset circuit is usedfor generating the built-in reset signal.
 5. The implantable biomedicalchip according to claim 1, wherein the modulator is a load-shift keyingmodulator.
 6. The implantable biomedical chip according to claim 5,wherein the modulator comprises: a transistor and a capacitance.
 7. Astate transition method for an implantable biomedical chip, comprisingthe steps of: (a) transiting a zero state to a first state according toa built-in reset signal; (b) transiting the first state to a secondstate according to a synchronization packet; (c) transiting the secondstate to a third state according to a start packet; and (d) transitingthe third state to the first state according to an end packet.
 8. Thestate transition method according to claim 7, wherein when the built-inreset signal is at high level, the zero state is transited to the firststate.
 9. The state transition method according to claim 7, furthercomprising a step of: transiting the first state to the zero state whenthe built-in reset signal is at low level.
 10. The state transitionmethod according to claim 7, further comprising a step of: transitingthe second state to the zero state when the built-in reset signal is atlow level.
 11. The state transition method according to claim 7, furthercomprising a step of: transiting the third state to the zero state whenthe built-in reset signal is at low level.